Alligator

Alligators are Archer's biggest fear. During the events of Pipeline Fever, Archer attempts fishing with a bow and arrow. Instead of shooting a fish, he accidentally shoots an alligator in the head. This enrages the gator and it attacks Archer and Lana aboard the airboat. As Archer attempts to shoot the gator, he misses and ends up shooting a hole in the deck of the Airboat.

As revealed in the episode Once Bitten, Archer received a stuffed alligator on his sixth birthday. These memories are triggered by a 'spirit journey' led by James Mason discovering much about Archer's psyche and why he is the way he is.